1. Field of the Invention
The present invention relates to an image forming apparatus of the electrophotographic system, which can form an image on a sheet.
2. Description of the Related Art
Recently, with the advancement of downsizing of image forming apparatuses of the electrophotographic system, a distance between a transfer portion and a fixing nip of the image forming apparatus is coming to be short. In such an apparatus, when the width of a sheet in a conveying direction becomes shorter than the distance between the transfer potion and the fixing nip, the sheet lies on both the transfer portion and the fixing nip. If the axial line of a transfer member forming the transfer portion in a longitudinal direction thereof is not parallel to the generatrix of the fixing nip, the sheet may curve along the generatrix of the fixing nip. Thus, an image formed on the sheet may be distorted so that a desired printed product cannot be obtained.
Thus, Japanese Patent Application Laid-Open No. 2004-144878 discusses a configuration for adjusting an alignment (degree of parallelization) between the transfer portion and the fixing nip. In this configuration, a fixing device is fixed to a sub-housing (drawer unit), which can be drawn out of a main housing (an apparatus body). In such a configuration, a user can adjust an alignment between the secondary transfer device and the fixing device by adjusting a position in which the sub-housing is stored.
However, there is the following issue when a user adjusts the storing position of the sub-housing (drawer unit) for adjusting alignment.
A fixing roller and a pressure roller in the fixing device are rotated by receiving driving force transmitted from a drive input gear attached at a backside plate of the image forming apparatus main body. In other words, the driving force is transmitted from a driving source provided on the apparatus main body with a gear provided in the fixing device meshing with the drive input gear.
In such a configuration, when a user adjusts a storing position of the sub-housing for adjusting an alignment between the transfer device and the fixing device, meshing between the gear provided the fixing device and the drive input gear may be changed. In other words, when a user adjusts an alignment between the transfer portion and the fixing nip, the adjustment may affect a rotation speed of the fixing device. For example, tooth traces of the drive input gear provided on the main-housing side and the gear provided on the sub-housing side deviate each other. Thus, the rotational driving force for rotating the fixing device may periodically change. As a result, unevenness in the rotation speed of the fixing device may occur.